This project is concerned with the molecular epidemiology of cancer. Many independent genetic events occur in the transformation from a normal cell to malignancy. Changes in genomic DNA occur at specific sites and can lead to activation of proto-oncogenes or inactivation of tumor suppressor genes through mutation, recombination, gene amplification, translocation, or other chromosomal abnormalities. In some human hereditary diseases, an increased incidence of neoplasia is correlated with a defect in the repair and/or replication of damaged DNA. Our ultimate objective is to understand how the processing of damaged DNA in mammalian cells relates to carcinogenesis. We are particularly interested in how human cells process DNA lesions through the respective pathways of global genomic excision repair (GGR) and transcription-coupled repair (TCR). While a deficiency in GGR is well-known to predispose to cancer, a defect in TCR, as in the hereditary disease Cockayne syndrome (CS), does not. The characteristic developmental and neurological problems in CS are thought to be a consequence of defective TCR of endogenous oxidative DNA damage. We have documented a TCR deficiency in "UV Sensitive syndrome" (UVSS), a hereditary disease that does not present the developmental/neurological features of CS. We propose to test our hypothesis that the UVSS gene product is essential for TCR through the nucleotide excision repair pathway but not through the base excision repair pathway that deals with oxidative DNA lesions. UVSS could be a key gene in the link between DNA repair and transcription. Our proposal includes the following sub-projects: (1) The role of TCR in repair of oxidative DNA lesions will be assessed in UVSS cells, using established methods for gene-specific repair. (2) Repair of other classes of DNA damage (e.g., Benzo[a]pyrene diol-epoxide) will be assessed, using monoclonal antibodies, 32P post-labeling, and gene specific repair assays, to further characterize the repair deficiency in UVSS cells. (3) Mutagenesis studies will be performed in UV-irradiated UVSS cells for comparison with those in CS. (4) The phenomenon of inhibited GGR in active or inactive genes in TCR-deficient cells will be further characterized. (5) A complementation assay will be used to characterize cells from photosensitive patients of unknown genotype, obtained from existing collections, for assignment to UVSS, CS, or other known or unknown syndromes. The results should enhance our understanding of the role of TCR in relation to human tumorigenesis and development. New genes implicated in TCR may be discovered. Novel interactions may be revealed that will clarify relationships between cellular DNA transactions.